Dark Matter Day 2022

Today is Dark Matter Day – a nice opportunity to present you a couple of scientists and groups involved in the research of this obscure subject. Welcome to the #CRESST, #COSINUS and #MADMAX labs!
#darkmatter #research #darkmatterday

[tonibat]

Best wishes to all hard working young physicists struggling to untie the DM knot.
A (delayed) present for those who are not too impressed by 'irrefutable evidence':

"Fluid Spacetime a MOND-Based Alternative Perspective on The Problems of Dark Matter Dark Energy and Black Holes". OSP Journal of Physics and Astronomy 3: JPA-3-138.

Dark matter exists, but might be very different from prevailing consensus.
A Fluid Spacetime mechanism provides consistent answers to dark matter and dark energy, postulates radical changes in our current understanding of black holes and gravity. The bullet cluster finds a rational simple explanation, as do the anomalous curvatures in clusters of galaxies, the mysterious Magorrian relation, and the weird departure from Keplerian orbits for stars orbiting Sgr A* black hole.
Of course, this comes at a price. Our interpretation of beloved Einst Equation E=mc2 must be reappraised. But then, what?
Happy Dark Matter day to you all !

[michaelkahn]

Einstein’s theory of General Relativity states that spacetime is curved by the presence of mass. This curvature influences the motion other objects with mass and gives rise to gravitation. Thus, gravity is a result of geometric features in spacetime.

However, we also observe gravitational effects – curvature of spacetime – in areas without any detectable mass. This has given rise to the concept of dark matter, which is matter that does not interact in any detectable way with normal matter, except through gravity. So, there is some large quantity of dark matter scattered throughout the universe, which curves spacetime and causes gravitational effects just like normal matter, but we cannot see or detect it with any known method.

An alternative theory to the identity of dark matter is proposed – it is not matter at all, but rather an intrinsic curvature of spacetime. In other words, spacetime is not naturally flat. Even in the absence of matter, we observe some inherent curvature of spacetime.

So, the question is now – why is spacetime naturally curved? Why is it not flat in the absence of mass?

The universe is 4-dimensional, with 3 spatial dimensions and one dimension in time. Rather than consider time as a linear dimension, we can consider it as a radial one. Therefore, rather than describing the universe with a Cartesian coordinate system, we describe it with a 4-dimensional spherical coordinate system – 3 angular coordinates, φ1, φ2, φ3, and one radial coordinate in time, t. We live on the 3-dimensional surface of a 4-dimensional bubble which is expanding radially in time. Thus, the Big Bang represents t=0, the beginning of time.

The crucial point is that the expansion of the universe is not homogeneous in all directions. The expansion rate at one point on the bubble’s surface may differ slightly from another point near it. The universe is only roughly spherical in 4 dimensions, the same way that the Earth is only roughly spherical in 3 dimensions. The same way we observe local mountains and valleys on the surface of Earth, we observe local “mountains” and “valleys” on the surface of the universe bubble. The inhomogeneity of the expansion of the universe has given rise to natural curvature of spacetime. This natural curvature causes the phenomenon of “dark matter”.

“Valleys” in spacetime pull matter in, similarly to the warping of spacetime of massive objects. So “dark matter” is really “valleys” in spacetime that are expanding slower than the regions surrounding it. These valleys tend to pull matter in and create planets, stars, and galaxies – regions of space with higher-than-average densities of mass. Conversely, “mountains” in spacetime will repel matter away, an “anti-gravitational” effect, which gives rise to cosmic voids in space where we observe no matter.

Each point on the surface of the universe bubble traces out a time arrow in 4-dimensional space, perpendicular to the surface. These time arrows are not parallel to each other since the universe is not flat. This causes points to have nonzero relative velocity away from each other. It is generally accepted that the universe is expanding faster than observable energy can explain, and this is expansion is believe to be still accelerating. The “missing” energy required to explain these observations has given rise to the theory of dark energy. The time dilation caused by non-parallel time arrows can be proposed as an explanation for dark energy. Alternatively, dark energy is real energy coming from potential energy gradients caused by non-parallel time arrows.

As a sanity check, we can calculate the expansion rate of the universe based on the universe bubble model. Since the radius of the universe bubble is expanding at the speed of light in the time direction, it increases at 1 light second per second. Therefore, the “circumference” of the 3-dimensional surface increases by 2π light seconds per second, or about 1.88*10^6 km/s. This expansion is distributed equally across the 3-dimensional surface, so the actual observed expansion rate is proportional to the distance from the observer. At present, the age of the universe is estimated to be 13.8 billion years, so the radius of the universe bubble is 13.8 billion light years, or about 4233 megaparsecs (3.26 million light years to 1 Mpc). Thus, we can calculate the expansion rate of the universe, per megaparsec from the observer, as:

Expansion rate =

[meghananagaraj]

I'm proud to see indians working on it, im behind dark matter looking to work in cern

[meghananagaraj]

Guys is there anyway to get me involved I'm presently research scholar in iit dhanbad, I want to work on dark matter, I'm looking for a right place for me